Coil buffing process and apparatus



1958 H. H. HOUDYSHELL ET AL 2,850,455

COIL BUFFING PROCESS AND APPARATUS Filed Aug. 5, 1957 2 Sheets-Sheet 1 4 48 a? ll! 3 I i 26 D I g lo 69 I I L9 ,39 a

/NVENTO/?S. HARRY H. HOUOYSHELL. CLAYTON O. GRIFFITH BY THl/l? ATTORNEYS. HARRIS, K/EcH, FOSTEK? & HA AR/S H. H. HOUDYSHELL ET AL COIL BUFFING PROCESS AND APPARATUS Nov. 18, 1958 2 Sheets-Sheet 2 Filed Aug. 5, 1957 2,860,455 Ullllh BUFFTNG PROCESS AND APPARATUS Harry H. Houdysheil, Pasadena, and Clayton 0. Griffith, Whittier, Calif, assignors to Beckman Instruments, Inc Fullerton, Calif, a corporation of California Application August 5, 1957, Serial No. 676,098 12 Claims. (Cl. 51-139) This invention relates to a method and apparatus for bufiing the inner surface of a continuous helical coil. The invention is especially adapted for use in removing electrical insulating material from the inner surface of such helical coils for use in helical potentiometers and the like.

In the manufacture of helical potentiometers, the very fine resistance wire is ordinarily wound on a cylindrical core to form a minor helix and, after being coated with an insulating varnish as a bonding agent, the wound core is formed into a helical coil, referred to as the major helix. It is now necessary to bare a portion of each turn of the wound resistance wire so that the moving contact later positioned within the major helix can complete an electrical circuit with the resistance wire. Since the helical coil is formed in a continuous operation and is produced in long sections, it is desirable to provide a method and apparatus for continuously buffing the inner surface of the coil prior to cutting the long coil into segments for insertion into potentiometer cases. Of course, the method and apparatus of the invention are equally adapted to use with short sections of helical coils and with helical coils which do not have a minor helix wound on the major helix.

It is an object of the invention to provide'a method and apparatus for bufling the inner surface of the helical coil in which a turn of the coil is threaded through an endless belt, the belt being driven with its inner surface engaging the inner surface of a turn of the coil. A further object is to provide means for supporting the coil for rotation about the axis of the helix, the coil being rotated by the action of the belt or by the rotation of the support or by a combination of the belt and the support.

It is a further object of the invention to provide a coil butfing method and apparatus in which that portion of the belt which engages the turns of the minor helix moves along the axis of the wire comprising the turns thus carrying loosened particles away from the unit without allowing such particles to be lodged between the turns of the minor helix and substantially eliminating side forces on the turns of the minor helix which tend to loosen the bond between the resistance wire and the core. A further object of the invention is to utilize a flexible or soft endless belt which covers at least several turns of the minor helix so that when the inner surfaces of the belt and the coil are brought into engagement with the belt moving substantially parallel to the axis of the resistance wire, the softer insulating material between turns of the minor helix will be removed to a point below the surface of the bare wire so that the insulating material will not interfere with movement of the wiper contact along the wire.

In carrying out the coil butfing of the invention the endless belt will ordinarily be treated with an abrasive material and it is an object of the invention to provide for passing the belt through a cleaning or other treating solution for controlling, improving, or modifying the abrasive action of the belt. A further object of the invention is to provide a coil buffing method and apparatus in which the bufiing operation may be carried out while submerged in a solution for controlling temperature, pressure, environment, abrasive content, and the like.

It is another object of the invention to provide control of the zone being buffed so that the amount of bare resistance wire is precisely determined, this control ordinarily being obtained by varying the shape of the loop of the endless belt which engages the turn of the helical coil. Another object of the invention is to provide a coil bufiing method and apparatus in which a belt having ends may be used in the same manner as an endless belt, such a belt preferably being quite long so that it may be driven in one direction for a period of time and then rewound or driven in the opposite direction.

The invention also comprises novel details of construction and novel combinations and arrangements of parts, which will more fully appear in the course of the following description. The drawings merely show and the description merely describes a preferred embodiment of the present invention which is given by way of illustration or example.

In the drawings:

Fig. l is a side view of a preferred form of apparatus for practicing the invention;

Fig. 2 is a top view of the embodiment of Fig. 1;

Fig. 3 is a partial sectional view taken along the line 3-3 of Fig. 1;

Fig. 4 is an enlarged the line 44 of Fig. 1;

Fig. 5 is an enlarged partial sectional view taken along the line 55 of Fig. 4;

Fig. 6 is a partial sectional view taken along the line 66 of Fig. 5; and

Fig. 7 illustrates the bufiing operation of the invention.

The apparatus illustrated in Figs. 1 and 2 includes an upstanding frame 10 mounted on a base plate 11. A plurality of pulleys is mounted on the frame 10 to provide a path for an endless belt 12. Pulleys 13, 14, 15, 16, 17, 18, and 19 are mounted on the frame by suitable pins, and pulleys 22, 23, and 24 are mounted on brackets 25, 26, and 27 respectively by similar pins. Each of the brackets is slidable relative to the frame provided with a slot 28 for receiving guide screws 29, 30 mounted in the frame, as exemplified by the bracket 25.

An upstanding loop 33 is formed in the belt 12 be partial sectional view taken along tween the pulleys 22, 23, the shape of the loop beingcontrolled by the position of the pulleys 22 and 23 rela-. tive to the remaining pulleys. The brackets 25 and 26 are ordinarily clamped against the frame 10 by the guide screws with the pulleys 22 and 23 in the desired position, but the bracket 27 is screws, it being urged to the right by a tension spring 34 fixed between the bracket and a pin 35 in the frame, thus controlling the tension in the belt 12.

The endless belt also passe over a pulley 38 of a drive mechanism consisting of a motor 39 and gear reduction unit 4%}, the motor being carried on the frame by a bracket 41.

When desired, a fluid container 44 may be mounted on the base plate 11 with the pulleys 15 and 16 positioned Within the container so that the belt will move through the container.

Means are provided for supporting a helical coil 45 permitting rotation of the coil about the axis of the helix. A preferred form is shown herein comprising a trough formed by parallel rolls 46, 47 which are supported at their ends in brackets 48, 49 projecting outward from the frame 10. Each of the rolls is preferably provided with spaced, enlarged sections 52, 53 defining a groove 10, each being ordinarily slidable on the guidethe width between the rolls 46, 47, this structure being best seen in Figs. 2 and 3. The roll 47 is journaled in blocks 54, 55 which slidably rest on the brackets 48, 49, respectively, the blocks being fixed to a bar 56 by pins 57, 58 which are slidably positioned in the frame 10. A drive screw 59 is rotatably mounted in the frame 16 and threadedly engages the bar 56 so that when the drive screw 59 is rotated, the bar 56, and hence the roll 47, are moved toward or away from the roll 46, thereby permitting adjustment for use of the apparatus with various sizes of helical coils.

Provision may be made for driving the rolls to produce rotation of the coil resting thereon. A drive motor 62 is mounted on the frame by a bracket 63 with screws 64 passing through slots 65 in the frame, the motor preferably being of the gear reduction type to provide a low output R. P. M. A pulley 66 on the shaft 'of the drive motor 62 and corresponding pulleys 67, 68 on the rolls 46, 47, respectively, are coupled by a belt 69 for driving the rolls. The slots 65 permit changing of the position of the drive motor when the spacing between the rolls is changed to maintain proper tension on the belt 69. Guide pins 70, 71 may be mounted in the frame 10 below the rolls if desired to serve as guides for the endless belt. 7

In the operation of the coil buffing apparatus, an end of the helical coil 45 is passed through the loop 33 of the endless belt 12 and the coil is then rested on the rolls with that portion of the coil which is engaged by the belt resting in the grooves between the enlarged sections 52, 53. The pulleys 22 and 23 are adjusted to provide the desired zone of contact between the belt and the turn of the coil for producing the desired amount of buffed surface on the coil. The zone of contact between the belt and the coil is shown in greatly enlarged form in Figs. 5 and 6. If desired, a belt with ends using feed and take-up reels could be substituted for the endless belt described above. When the end of the preferably long belt is reached, the drive may be reversed, or the reels interchanged, or the belt rewound.

The endless belt 12 preferably is formed of or carries an abrasive material to improve the buffing operation and it is preferred to use a silicone rubber belt thoroughly impregnated with a uniform mixture of pumice or the like. In Figs. 5, 6, and 7, such a belt is shown with its inner surface 74 loaded with abrasive particles. When in operation, the endless belt tends to carry away the abrasion products of both the belt and the object being abraded or buffed, thus providing a relatively clean belt surface on the work. When desired, a cleaning or other treating solution can be placed in the container 44 for controlling, improving and modifying the abrasive action of the belt. Examples of such treating solutions are water, alcohol, chlorethene, sodium bicarbonate slurry, and the like.

As the belt is driven by the motor 39, the rolls on which the coil rests may also be driven slowly by the motor 62 thus advancing the coil through the loop of the belt providing continuous bufiing of the inner surface of the coil by the inner surface of the belt. If the direction of motion of the belt as it contacts the coil is made slightly oblique to the axis of the coil, the motion of the belt will also tend to cause the coil to rotate and when desired, the drive motor 62 may be eliminated.

This coil bufiing method and apparatus are often used with the helical coil for a helical potentiometer, the coil including a small diameter resistance wire 75 wound in the form of a minor helix on a core 76, which may also be wire, the core bing formed into a major helix (Figs. 4-7). The wire 75 which forms the minor helix usually has a coating 77 of insulating material, as seen in the right-hand portion of Fig. 6, and the core 76 with the wire 75 wound thereon is usually also provided with a coating 78 of insulating material, as shown in the left portion of Fig. 6, to further improve the insulating properties of the structure and to bond the turns of the minor helix in place. Of course, the invention is equally adapted for use with such structures where one or the other or both of the insulating coatings are not utilized.

That portion of the belt which contacts the coil moves along the axis of the resistance wire rather than transverse to its axis and thereby carries wear particles away from the coil without allowing such particles to become lodged between the turns of the minor helix. Furthermore, this substantially parallel movement of the belt produces very little, if any, side forces on the turns of resistance wire and thus substantially eliminates any tendency for the buffing action to loosen the turns of the minor helix. The endless belt 12 is preferably made of a flexible, soft material and is made wide enough to cover at least three turns of the minor helix and preferably two or three times that many. When the inner surface of the flexible belt is urged against the under surface of the helical coil, the surface of the belt will conform to the surface of the coil as seen in the upper portion of Fig. 6, removing the relatively softer insulating material to a depth below the surface of the harder resistance wire thus preventing the insulating material from interfering with movement of the wiper contact along the bare surface of the turns of resistance Wire.

The minor helix of resistance wire on the core has a finite though small pitch so that even when the belt moves in a direction parallel to the axis of the major helix, the engagement of the belt with the coil will tend to rotate the coil about the axis of the major helix. This method for rotating the coil may be used alone or in conjunction with the motor drive for the rolls which support the coil.

The method and apparatus of the invention may be used for buffing coals of various size ranges of both minor and major helixes in various combinations of pitches. The buffing rate can be controlled by varying the speed of the belt and/ or by varying the quantity and type of abrasive material utilized. In the apparatus illustrated herein, the actual buffing operation occurs at a point in space permitting visual observation of the operation and providing ease of ventilation and cooling. If desired, the buffing operation may be carried out with the components submerged in a liquid providing additional temperature and/ or abrasion control.

Although an exemplary embodiment of the invention has been disclosed and discussed, it will be understood that other applications of the invention are possible and that the embodiment disclosed may be subjected to various changes, modifications, and substitutions without necessarily departing from the spirit of the invention.

We claim as our invention:

1. In a method of buffing the inner surface of a plurality of turns of a heical coil with an endless belt, the steps of: threading one end of the coil through the belt; driving the belt; forcing the inner surface of a portion of the moving belt against the inner surface of a portion of a turn of the coil; and rotating the coil about its axis.

2. In a method of bufiing the inner surface of a plurality of turns of a continuous helical coil with an endless belt, the steps of: inserting the leading end of the coil through the belt; driving the belt along a predetermined path; forcing the inner surface of a portion of the moving belt against the inner surface of a portion of a turn of the coil with the direction of motion of a portion of the belt in contact with the coil substantially parallel to the axis of the helix; and rotating the coil about its axis.

3. In a method of buffing the inner surface of a plurality of turns of a helical coil with a belt, the steps of: forming a loop in the belt; threading one end of the coil through the loop; driving the belt; forcing the inner surface of the loop of the moving belt against the inner surface of. aportion of aturn of the coil; and rotating the coil about its axis.

7 4. In a method of buffing with an endless belt the 8 inner surface of a plurality of turns of a helical coil comprising a wire wound as a minor helix on a helical core as the major helix, the steps of: threading one end of the coil through the belt; driving the belt; forcing the inner surface of a portion of the moving belt against the inner surface of a portion of a turn of the coil with the direction of motion of a portion of the belt in contact with the coil substantially parallel to the axis of the major helix; and rotating the coil about-the axis of the major helix.

5. In a method of bufiing with a flexible endless belt the inner surface of a plurality of turns of a continuous helical coil comprising a wire wound as a minor helix on a helical core as the major helix with the wire bonded to the core by an insulating material, the steps of: threading one end of the coil through the belt; supporting the coil for rotation about the axis of the major helix; driving the belt along a predetermined path; and forcing the inner surface of a portion of the moving flexible belt against the inner surfaces of a plurality of adjacent turns of the minor helix removing insulating material from said inner surfaces and from between said turns, with that portion of the belt in contact with said turns of the wire moving along the axis of the wire.

6. In an apparatus for bufling the inner surface of a plurality of turns of a helical coil, the combination of: an endless belt; means for driving the belt; means for supporting the coil for rotation about the axis of the helix with a turn of the coil passing within a loop of said belt; and means for bringing the inner surface of the moving belt into contact with the inner surface of a turn of the coil.

7. In an apparatus for bufling the inner surface of a plurality of turns of a helical coil, the combination of: a belt; means defining a path for said belt, said path including a loop; means for driving the belt along said path; means for supporting the coil for rotation about the axis of the helix with a turn of the coil passing within said loop; and means for bringing the inner surface of the loop portion of the moving belt into contact with the inner surface of a turn of the coil.

8. In an apparatus for bufiing the inner surface of a plurality of turns of a helical coil, the combination of: an endless belt; means for driving the belt along a path; means for rotating the coil about the axis of the helix with a turn of the coil passing within a loop of said belt; and means for bringing the inner surface of the moving belt into contact with the inner surface of a turn of the coil with a portion of the belt in contact with the coil moving in a direction substantially parallel to the axis of the helix.

9. In an apparatus for bufling the inner surface of a plurality of turns of a helical coil, the combination of:

an endless belt; means for driving said belt; trough means providing a slot with a loop of said belt passing therethrough, said trough means being adapted to support the coil for rotation about the axis of the helix with a turn of the coil passing through said loop; means for forcing the inner surface of said loop into engagement with a portion of the inner surface of a turn of the coil; and means for changing the shape of said loop to vary the portion of the inner surface engaged by said loop.

10. In an apparatus for buffing the inner surface of a plurality of turns of a helical coil, the combination of: an abrasive carrying endless belt; means for driving the belt along a path; means for supporting the coil for rotation about the axis of the helix with a turn of the coil passing within a loop of said belt; means for bringing the inner surface of the moving belt into contact with the inner surface of a turn of the coil; and a fluid container disposed along said path for passage of said belt therethrough.

11. In an apparatus for bufling the inner surface of a plurality of turns of a helical coil, the combination of: an endless belt; means for driving said belt; two parallel rolls for supporting the coil thereon with a turn of the coil passing within a loop of said belt, said rolls including means for limiting movement of the coil along the axis of said rolls; means for rotating both of said rolls in the same direction; and means for bringing the inner surface of the moving belt into contact with the inner surface of a turn of the coil with a portion of the belt in contact with the coil moving in a direction substantially parallel to the axis of the helix.

12. In an apparatus for removing insulating material from the inner surface of a plurality of turns of a helical coil having a wire wound as a minor helix on a core in the form of a major helix with the wire bonded to the core by an insulating material, the combination of: an abrasive carrying, flexible, endless belt, said belt being Wider than three times the diameter of the wire; means for driving said belt along a path, said path including a loop; means for supporting the coil for rotation about the axis of the major helix with a turn of the coil passing through said loop; means for forcing the inner surface of said loop of the moving belt into engagement with a portion of the inner surface of a turn of the coil; and means for changing the shape of said loop to vary the portion of the inner surface engaged by said loop.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,860,455 November 18, 1958 Harry He Houdyshell et al It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 18, for "under surface" read w inner surface Signed and sealed this 24th day of February 1959.

XSEAL) ttest:

KARL HY. AXLINE Commissioner of Patents 

